The quality of a semiconductor is directly dependent on the consistency of the fabrication process by which it is created. Specifically, production of state-of-the-art semiconductor components requires reproducible plasma processes for etching and deposition. Controls on chemical composition and impurity levels within the fabrication chamber are crucial to the success of these processes, particularly at today's increasingly high levels of circuit density.
Certain analytical techniques have been demonstrated as potential monitors of chemical species in a plasma process. These techniques include optical emission spectroscopy (OES), fourier transform infrared spectroscopy (FTIR), and laser induced fluorescence (LIF). Each technique offers unique information about a processing environment. However, each of these analytical approaches characterizes gaseous species by determining an intensity for one or more electromagnetic wavelengths occurring at the same point in time within the plasma chamber.
In the specific inventive embodiments of semiconductor fabrication described herein, an optical emission spectrometer (OES) is utilized as the sensor of choice. An OES is a commercially available device which is used to detect the presence and relative concentrations of various gases in a plasma chamber. This spectrometer works by detecting light emitted from electron transitions occurring in atoms and molecules within the chamber. Currently, optical emission spectrometers are used in open-ended processing whereby an expert attempts to characterize the chemistry of a plasma environment during wafer manufacturing, e.g., to identify a processing end-point based on the resultant data. Existing OES processing is discussed further herein below. Also, additional information thereon is available in an article by G. Gifford, entitled "Applications of Optical Emissions Spectroscopy in Plasma Manufacturing Systems," SPIE Microelectronic Integrated Processing Symposium (1990).
It is important to note that currently each of the above-listed spectroscopic techniques for possible use in semiconductor manufacturing requires an expert to analyze an initial spectra and to train manufacturing personnel in the meaning of the spectra and that of deviations from base line spectra measurements. Such an inherently subjective method of analysis can often be inadequate due to the complexity of the spectra involved. Also, these open-ended analysis techniques cannot be used to effectively execute real-time monitoring and control of the manufacturing process. In fact, there are few real-time, closed loop monitoring and control methods/systems presently employed in the semiconductor manufacturing environment.
Thus, to summarize, there is a need in the art for a more effective technique for monitoring and controlling semiconductor fabrication. The present invention addresses this deficiency by providing an automated, closed loop, real-time method and system for monitoring and controlling semiconductor fabrication processing within a plasma chamber.